Tube shielding



July 29, 1958 J. H. LANGWORTHY ET AL 2,

TUBE SHIELDING Filed March 17, 1952 FIG. 3

FIG. 2

INVENTORS JAMES H. LANGWORTHY By R088 A QUINN ATTORNEY United States Patent h. in

TUBE SHIELDING James H. Langworthy, Long Beach, and Ross A. Quinn,

Palo Alto, Calif., assignors to North American Aviation, Inc.

Application March 17, 1952, Serial No. 277,046

2 Claims. (Cl. 174-35) This invention relates to tube shielding, and particularly to methods and meansfor rapidly conducting heat away from shielded miniature electronic tubes.

The sensitive elements enclosed within miniature tubes must be shielded from stray electrostatic fields which disturb the normal operation of the tubes. A grounded metal shield can be clamped around the glass envelope of the miniature tube, or a shield can be constructed inside the envelope, thereby shielding the sensitive elements from stray electrostatic fields. One disadvantage of these types of shielding is the resultant operation of the tube at a higher temperature than normal, thereby changing the characteristics of the tube. The operating life of the tube varies with the operating temperature. Longer life is obtained by operation at a lower temperature. This increase in operating temperature is caused by the reflection of the filament radiation back into the sensitive elements by the inner surface of the shield. Clamping a shield around the envelope has an added disadvantage of increasing the risk of breaking the glass envelope.

It is therefore an object of this invention to provide means for conducting heat rapidly away from shielded electronic tubes.

It is another object of this invention to provide means for obtaining greater mechanical strength of miniature electronic tubes.

It is a further object of this invention to provide a method of conducting heat rapidly away from shielded electronic tubes.

It is a further object of this invention to provide a method of easily mounting miniature electronic tubes.

It is another object of this invention to provide an electrostatic shield for a miniature electronic tube.

Other objects of invention will become apparent from the following description taken in connection with the accompanying drawings, in which Fig. 1 is a side view of the shielded miniature tube mounted to a chassis in the preferred manner of the invention;

Fig. 2 is a sectional view of the shielded tube of Fig. 1 taken along lines 2-2;

And Fig. 3 is a sectional view of a second embodiment of the invention.

Referring to the drawings, glass envelope 1 of the miniature tube encloses sensitive tube elements 2. Multiple leads 3 electrically connect sensitive tube elements 2 through one end of glass envelope 1 to appropriate external circuit elements (not shown). This invention contemplates covering glass envelope 1 with a coating 4. Coating 4 should have a high infrared absorption characteristic and should have a suitable binder which will adhere to glass envelope 1. A coating composed of a colloidal suspension of defiocculated graphite in water has been used satisfactorily. Coating 4 is applied by dipping, painting, or other appropriate means. A small area immediately surrounding leads 3 is left uncoated to prevent short circuiting leads 3.

It is further contemplated by this invention to electro- 23 plate a thick metal shell 5 over the coating 4. An electroplated shell of copper has been used satisfactorily. In the preferred form of shielded tube shown in Fig. 2, coating 4 is a heat absorbent material which is also a good electrical conductor. Electroplating on a coating made with this type of material is easily accomplished by methods well known in the art.

In the second embodiment of shielded tube shown in Fig. 3, coating 4 is a heat absorbent material which is a poor electrical conductor. To provide the conductivity required for electroplating, a layer 6 of good conducting material is chemically reduced on coating 4. The chemically reduced layer 6 is applied by inserting the coated tube in a solution of silver salt and a reducing agent until a thin silver layer is formed over the coating. The tube is .then electroplated by methods well known in the art. The thickness of the electroplated shell is dependent on the desired rate of conduction of heat away from the tube and on the desired mechanical strength of the shielded tube.

The shielded tube is mounted on a supporting plate or chassis 7 by soldering. A considerable saving of time is accomplished by mounting all the shielded tubes on the chassis by one soldering operation. The shielded tube mounted to chassis 7, as described, has a much higher rate of heat dissipation than a tube having a shield clamped around the envelope. Coating 4, by absorption of the filament radiation, prevents a large portion of the radiation which passes through glass envelope 1 from being reflected back into tube elements 2. If this radiant heat absorbed by coating 4 is rapidly conducted away, the tube will operate at a low temperature. The rate of heat dissipation depends on the total surface area exposed to the atmosphere. The method and means contemplated by this invention makes available the combined surface area of the shell and of the chassis for dissipation of this heat.

The electroplated metal shell 5 contemplated by this invention performs several functions. It provides an electrostatic shield around the tube so that other circuit elements can now be positioned Within line of sight of the tube without affecting tube operations. Circuit elements which are sensitive to heat radiation may be positioned near the tube since the shield absorbs the tube radiation. The shell 5 also prevents easy breakage of glass envelope 1 by greatly increasing the mechanical strength of the tube. The shield is also made thick enough to conduct heat rapidly away from coating 4. When the shell is soldered to chassis 7 the heat generated by operation of the tube is rapidly dissipated, since the combined surface areas of the shell and the chassis are available for dissipation of heat.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by Way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. In combination with a heat conductive chassis, means for shielding a glass-shelled electronic tube and for maintaining said tube at a low operating temperature comprising a first coating covering substantially entirely the outer surface of the shell of said tube and in intimate contact therewith, said first coating being composed of material having a high radiant heat and infrared absorbent characteristic and good heat conduction properties and an electrostatic shield of metallic material covering substantially entirely said first coating and in intimate contact therewith, means to transfer heat from said shield to said chassis comprising metallic means uniting said shield and said chassis along substantially the entire length of said shield, whereby heat radiated from said tube is absorbed by said first coating, conducted to said shield and dissipated by conduction through said lastmentioned means.

2. Means for shielding an electronic tube as recited in claim 1 in which said first coating is a colloidal suspension of deflocculated graphite.

References Cited in the file of this patent UNITED STATES PATENTS 4 Baranowski Mar. 22, 1933 Friend Sept. 3, 1935 Muller Oct. 26, 1937 Harr Apr. 15, 1947 Gowell May 13, 1947 Posen Nov. 18, 1947 Lamphere Sept. 14, 1948 Khouri et al. Ian. 3, 1950 Seal et a1. June 9, 1953 FOREIGN PATENTS Great Britain July 9, 1945 

